The Evaluation of the Aedes Albopictus Entomological Index Based on the Topography to Compute the Essential Requirements for Dengue Transmission Surveillance in Nakhon Si Thammarat, Thailand

Abstract

An entomological index is widely used for determining dengue transmission and mosquito populations. In this study, we determined the association between Aedes albopictus mosquito counts in three areas with different topographical features from six districts in Nakhon Si Thammarat and infected patients reported by the Ministry of Public Health's Department of Disease Control, using entomological indices, such as the sticky pad index and the sweep net index. The sampling region was selected from the top six districts of the province based on the number of reported dengue cases per 100,000 people. The regions were Khanom, Mueang, Pak Phanang, Phrom Khiri, Thung Song, and Thung Yai. They were divided into three categories of geographical features, including city, beach, and mountain. The mosquitos were collected by walking in a star form inside a 5 m diameter circle. The mosquitoes were separated into groups based on their species, and the percentile of the index was computed. We found that the number of mosquitoes was the highest in Pak Phanang and lowest in Khanom. The two indices and the number of A. albopictus collected from the six sampling locations were not significantly different (t = 1.31, p > 0.05). The coastline region had the highest number of mosquitoes and was substantially different from the other two regions (cosmopolitan and mountain) (F = 4.30; p < 0.05). By performing Pearson's correlation analysis, we found a negative correlation between dengue cases and the entomological index (r = -0.472; N = 36). Similarly, the number of patients showed a negative correlation with relative humidity (r = -0.355) but a positive correlation with temperature (r = 0.064). The epidemic pattern shifted throughout the year, and the number of cases then increased 2-4 weeks after the insect was found.